Several methods have been investigated for synthesis of nanoparticles, such as ion implantation and annealing, or thermal decomposition of precursor gases. However, invariably there is the difficulty of ensuring the uniformity of nanoparticles size and inter-particle separation in the final device. Therefore, a method of synthesis for gold and other metal nanospheres embedded in an insulating matrix with great control over size, particle separation, and insulator thickness is favorable. Additionally, the control over nanosphere/nanowire synthesis location and orientation that allows finished MOS memory devices to be created in dense or sparse arrays would also be favorable.
Numerous methods have been developed for synthesis of semiconductor and metal nanoparticles. For example, highly luminescent semiconductor (CdSe, ZnS) quantum dots have been synthesized in ZrO, —SiO, hybrid sol-gel films using an organometallic approach. Traditionally, colloidal suspensions of metal nanoparticles have been formed by citrate reduction in aqueous solutions. In colloidal suspensions, the major difficulty is to achieve highly mono dispersive size distribution. Even so, gold particles in ˜1-200 nm diameter range are commercially available (Nanoprobes, Goldmark Biologicals). A tight size distribution has been observed for each of two assemblies analyzed. Closely-packed, self-assembled mono-layers of alkanethiol stabilized nanoparticles have also been reported using solvent evaporation. In this case, the length of the organic ligand defines the interparticle separation. Finally, self-assembly methods in combination with advanced lithography methods have also been reported.